Oxygen scavenging compositions comprising polymers derived from benzenedimethanol monomers

ABSTRACT

Herein is disclosed an oxygen scavenging composition, comprising (i) an oxygen scavenging polymer comprising structure I:
 
 X—R—X—O—CH 2 —Ar—CH 2 —O ,  (I)
 
     wherein —R— is selected from the group consisting of C 1 –C 24  alkyl, C 1 –C 24  substituted alkyl, C 6 –C 24  aryl, and C 6 –C 24  substituted aryl; —Ar— is selected from the group consisting of C 6 –C 24  aryl and C 6 –C 24  substituted aryl; and —X— is selected from the group consisting of null and —C(═O)—; (ii) a transition metal oxidation catalyst; and (iii) an energy-absorbing compound selected from the group consisting of microwave reactive materials and photoinitiators having a wavelength of maximum absorption of electromagnetic radiation from about 200 nm to about 750 nm. The oxygen scavenging composition can be used to form an oxygen barrier packaging article.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of oxygenscavenging compositions. More particularly, it concerns oxygenscavenging compositions comprising polymers derived frombenzenedimethanol monomers.

2. Description of Related Art

It is well known that limiting the exposure of oxygen-sensitive productsto oxygen maintains and enhances the quality and shelf-life of theproduct. For instance, by limiting the oxygen exposure of oxygensensitive food products in a packaging system, the quality of the foodproduct is maintained, and food spoilage is avoided. In addition suchpackaging also keeps the product in inventory longer, thereby reducingcosts incurred from waste and restocking.

Approaches for minimizing the oxygen exposure of packaged products cangenerally be grouped into two categories. One set of approaches involvesscavenging oxygen present in the package as a result of the packagingprocess. The other set of approaches involves minimizing the entry ofoxygen into the package during or after the packaging process.

Minimizing the entry of oxygen into the package after packaging can bepursued by forming one or more layers of the package from a polymerknown to possess oxygen barrier properties. Ethylene/vinyl alcoholcopolymer (EVOH) has very good oxygen barrier properties, but its oxygenbarrier properties are sensitive to moisture and it is relativelyexpensive. Polyethylene terephthalate (PET) does not have the latterdisadvantages, but its oxygen barrier properties are not as good asthose of EVOH. Therefore, there is interest in preparing modified PET orblends of PET with other polymers that may have better oxygen barrierproperties than PET alone without suffering from other shortcomings.

One approach that has been attempted is the blending of PET with anoxygen scavenging polymer. The oxygen scavenging polymer would scavengeoxygen that the PET would otherwise permit to pass from the environmentto the package contents. An example of this approach is reported byCochran et al., U.S. Pat. No. 5,021,515 (“Cochran”), which reports apackage comprising a layer comprising a blend of 96 wt % PET, 4 wt %poly(m-xylyleneadipamide) (MXD6), and 200 ppm cobalt. The PET providesoxygen barrier properties; the MXD6 provides oxygen scavengingproperties; and the cobalt catalyzes oxygen scavenging by the MXD6.

However, the package of Cochran has a number of shortcomings. First, PETand MXD6 are somewhat incompatible, and as a result, the clarity of atransparent bottle comprising this layer will deteriorate over time.Second, the compounding process requires an undesirably high processingtemperature because of the incompatibility issue described above as wellas the relatively high melting point of MXD6 relative to PET. Third, anextra thermal solidating process is often required to provide adequateoxygen scavenging performance of the PET/MXD6 blend.

Therefore, it is desirable to have a composition comprising PET andoxygen scavenging moieties with superior compatibility and ease ofprocessing. Such a composition would be expected to impart superiorphysical properties to a package, especially a bottle, made therefrom.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to an oxygen scavengingcomposition, comprising:

an oxygen scavenging polymer comprising structure I:

X—R—X—O—CH₂—Ar—CH₂—O

,  (I)

wherein —R— is selected from the group consisting of C₁–C₂₄ alkyl,C₁–C₂₄ substituted alkyl, C₆–C₂₄ aryl, and C₆–C₂₄ substituted aryl; —Ar—is selected from the group consisting of C₆–C₂₄ aryl and C₆–C₂₄substituted aryl; and —X— is selected from the group consisting of nulland —C(═O)—;

a transition metal oxidation catalyst; and

an energy-absorbing compound selected from the group consisting ofmicrowave reactive materials and photoinitiators having a wavelength ofmaximum absorption of electromagnetic radiation from about 200 nm toabout 750 nm.

In still another embodiment, the present invention relates to an oxygenbarrier packaging article, comprising an oxygen barrier layercomprising:

an oxygen scavenging polymer comprising structure I, as described above;

a transition metal oxidation catalyst; and

an energy-absorbing compound selected from the group consisting ofmicrowave reactive materials and photoinitiators having a wavelength ofmaximum absorption of electromagnetic radiation from about 200 nm toabout 750 nm.

In yet another embodiment, the present invention relates to a method ofinitiating oxygen scavenging by an oxygen scavenging composition,comprising:

-   -   (a) providing an oxygen scavenging composition, comprising:        -   (i) an oxygen scavenging polymer comprising structure I, as            described above;        -   (ii) a transition metal oxidation catalyst; and        -   (iii) an energy-absorbing compound selected from the group            consisting of microwave reactive materials and            photoinitiators having a wavelength of maximum absorption of            electromagnetic radiation from about 200 nm to about 750 nm;            and

(b) exposing the oxygen scavenging composition to electromagneticradiation for a duration sufficient to initiate oxygen scavenging by theoxygen scavenging composition.

The present invention provides an oxygen scavenging composition whichhas superior compatibility between its components, and packagingarticles comprising oxygen barrier layers comprising the oxygenscavenging composition which have superior oxygen barrier and physicalproperties.

DESCRIPTION OF DRAWINGS

FIG. 1 shows oxygen consumption as a function of time for an oxygenscavenging film comprising poly(benzenedimethanol adipate), as describedby Example 2.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In one embodiment, the present invention relates to an oxygen scavengingcomposition, comprising:

an oxygen scavenging polymer comprising structure I:

X—R—X—O—CH₂—Ar—CH₂—O

,  (I)

wherein —R— is selected from the group consisting of C₁–C₂₄ alkyl,C₁–C₂₄ substituted alkyl, C₆–C₂₄ aryl, and C₆–C₂₄ substituted aryl; —Ar—is selected from the group consisting Of C₆–C₂₄ aryl and C₆–C₂₄substituted aryl; and —X— is selected from the group consisting of nulland —C(═O)—;

a transition metal oxidation catalyst; and

an energy-absorbing compound selected from the group consisting ofmicrowave reactive materials and photoinitiators having a wavelength ofmaximum absorption of electromagnetic radiation from about 200 m toabout 750 nm.

It has been observed that a polymer comprising structure I is capable ofscavenging oxygen, and thus, in addition to other applications, isuseful in oxygen scavenging or active oxygen barrier packagingapplications. Though not to be bound by theory, it is believed that apolymer comprising structure I scavenges oxygen by undergoing benzylicoxidation. Though not to be bound by theory, the resulting product isbelieved to be very stable, and as a result, fragmentation of thepolymer does not occur, at least to any significant extent. Further, apolymer comprising structure I is a polyether or polyester, and as aresult, will be highly compatible with a polyether or polyester,respectively, added to the composition, either by chemical bonding tothe polymer or blending. In addition, the melting point of a polymercomprising structure I will typically be below the melting point ofpolyethylene terephthalate (PET), and thus, if processed with PET, nochange in the process temperature would be expected to be necessary.

As used herein, the term “alkyl” refers to any organic moiety whereinall carbon-carbon bonds are single bonds. Alkyl moieties can be linear,branched, cyclic, or polycyclic moieties. The term “aryl” refers to anyorganic moiety comprising at least one aromatic ring. Any carbon atomsin an aryl moiety, as defined herein, that are not part of the aromaticring or rings can be in an alkyl structure bound to an aromatic ring,wherein the alkyl structure meets the definitions of “alkyl” givenabove.

The term “substituted,” as used herein, refers to a moiety comprisingcarbon, hydrogen, and at least one other element. Preferably, the otherelement is selected from oxygen, nitrogen, silicon, sulfur, or halogen.Two or more elements other than carbon and hydrogen can be included.

In one preferred embodiment, —X—R—X— is a terephthalic acid moiety. Inone preferred embodiment, —X—R—X— is an adipic acid moiety.

The polymer may consist essentially of units having structure I. By“consists essentially” in this context is meant that at least about 95mol % of units of the polymer have structure I. In one preferredembodiment, at least about 99 mol % of units of the polymer havestructure I.

In another embodiment, the polymer further comprises units other thanstructure I. In one preferred embodiment, the other units are ethyleneterephthalate moieties.

The proportion of units having structure I to other units is from 1:99mol % to 99:1 mol %. Preferably, the proportion of units havingstructure I to other units is from about 5:95 mol % to about 95:5 mol %.More preferably, the proportion of units having structure I to otherunits is from about 10:90 mol % to about 90:10 mol %.

The polymer of the oxygen scavenging composition may, by way of exampleand not to be construed as limiting, be a homopolymer of units havingstructure I; a copolymer of units having structure I and other units;and a terpolymer of units having structure I and two other units; amongothers.

Copolymers, terpolymers, and higher order polymers can be random orblock polymers.

Preferably, the polymer is a copolymer of units having structure I andethylene terepthalate units. This polymer may be referred to herein as“benzenedimethanol PET.” The term “benzenedimethanol” is meant toinclude the 1,2-; 1,3-; and 1,4-isomers.

The oxygen scavenging composition further comprises a transition metal.The transition metal functions to catalyze oxygen scavenging by theoxygen scavenging polymer, increasing the rate of scavenging andreducing the induction period. Though not to be bound by theory, usefultransition metals include those which can readily interconvert betweenat least two oxidation states. See Sheldon, R. A.; Kochi, J. K.;“Metal-Catalyzed Oxidations of Organic Compounds” Academic Press, NewYork 1981.

Preferably, the transition metal is in the form of a salt, with thetransition metal selected from the first, second or third transitionseries of the Periodic Table. Suitable metals include, but are notlimited to, manganese, iron, cobalt, nickel, copper, rhodium, andruthenium. The oxidation state of the metal when introduced need notnecessarily be that of the active form. The metal is preferably iron,nickel, manganese, cobalt or copper; more preferably manganese orcobalt; and most preferably cobalt. Suitable counterions for the metalinclude, but are not limited to, chloride, acetate, oleate, stearate,palmitate, 2-ethylhexanoate, neodecanoate, or naphthenate, preferablyC₁–C₂₀ alkanoates. Preferably, the salt, the transition metal, and thecounterion are either on the U.S. Food and Drug Administration GRAS(generally regarded as safe) list, or exhibit substantially no migrationfrom the packaging article to the product (i.e. less than about 500 ppb,preferably less than about 50 ppb, in the product). Particularlypreferable salts include cobalt oleate, cobalt stearate, cobalt2-ethylhexanoate, and cobalt neodecanoate. The metal salt may also be anionomer, in which case a polymeric counterion is employed. Such ionomersare well known in the art.

Typically, the amount of transition metal may range from 0.001 to 1% (10to 10,000 ppm) of the oxygen scavenging composition, based on the metalcontent only (excluding ligands, counterions, etc.).

The oxygen scavenging composition may also comprise an energy-absorbingcompound selected from the group consisting of microwave reactivematerials and photoinitiators having a wavelength of maximum absorptionof electromagnetic radiation from about 200 nm to about 750 nm. Thoughnot to be bound by theory, it is believed that energy-absorbingcompounds of the group defined above absorb electromagnetic radiationand at least some of the energy of the electromagnetic radiationactivates a chemical process or processes that induces oxygen scavengingby the oxygen scavenging polymer of the composition.

In situations where the energy-absorbing compound is a photoinitiator,the photoinitiator will have a wavelength of maximum absorption ofelectromagnetic radiation (meaning a wavelength at which the extinctioncoefficient of the photoinitiator is higher than at any otherwavelength) from about 200 nm to about 750 nm. Electromagnetic radiationin this range of wavelengths is readily produced by apparatus that canbe conveniently included into package-formation or -filling procedures.Electromagnetic radiation in this range of wavelengths may also provideother useful activities, such as sterilizing a package prior to fillingor activating other chemical reactions in the package which may bedesired by the user.

Suitable photoinitiators are well known to those skilled in the art.Specific examples include, but are not limited to, benzophenone,o-methoxybenzophenone, acetophenone, o-methoxy-acetophenone,acenaphthenequinone, methyl ethyl ketone, valerophenone, hexanophenone,α-phenyl-butyrophenone, p-morpholinopropiophenone, dibenzosuberone,4-morpholinobenzophenone, benzoin, benzoin methyl ether,4-omorpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone,4′-methoxyacetophenone, α-tetralone, 9-acetylphenanthrene,2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene,3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene,thioxanthen-9-one, xanthene-9-one, 7-H-benz[de]anthracen-7-one, benzointetrahydropyranyl ether, 4,4′-bis(dimethylamino)-benzophenone,1′-acetonaphthone, 2′-acetonaphthone, acetonaphthone and2,3-butanedione, benz[a]anthracene-7,12-dione,2,2-dimethoxy-2-phenylacetophenone, α,α-diethoxyacetophenone, andα,α-dibutoxyacetophenone, among others. Singlet oxygen generatingphotosensitizers such as Rose Bengal, methylene blue, and tetraphenylporphine may also be employed as photoinitiators. Polymeric initiatorsinclude poly(ethylene carbon monoxide) andoligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone].

Due to the high cost of photoinitiators, it is desirable to use theminimum amount of photoinitiator required to initiate oxygen scavenging.This minimum amount will vary depending on the photoinitiator used, thewavelength and intensity of ultraviolet light used to initiate, andother factors. Preferably, the photoinitiator is either on the U.S. Foodand Drug Administration GRAS (generally regarded as safe) list, orexhibits substantially no migration from the packaging article to theproduct (i.e. less than 50 ppb in the product).

Photoinitiators that are especially useful in the present inventioninclude benzophenone derivatives containing at least two benzophenonemoieties, as described in U.S. Pat. No. 6,139,770. These compounds actas effective photoinitiators to initiate oxygen scavenging activity inthe oxygen barrier layer of the present invention. Such benzophenonederivatives typically have a very low degree of extraction from theoxygen barrier layer, which may lead to reduced malodor or off-taste ofa packaged food, beverage, or oral pharmaceutical product by extractedphotoinitiator.

A “benzophenone moiety” is a substituted or unsubstituted benzophenonegroup. Suitable substituents include alkyl, aryl, alkoxy, phenoxy, andalicylic groups contain from 1 to 24 carbon atoms or halides.

The benzophenone derivatives include dimers, trimers, tetramers, andoligomers of benzophenones and substituted benzophenones.

The benzophenone photoinitiators are represented by the formula:A_(a)(B)_(b)

wherein A is a bridging group selected from sulfur; oxygen; carbonyl;—SiR″₂—, wherein each R″ is individually selected from alkyl groupscontaining from 1 to 12 carbon atoms, aryl groups containing 6 to 12carbon atoms, or alkoxy groups containing from 1 to 12 carbon atoms;—NR′″—, wherein R′″ is an alkyl group containing 1 to 12 carbon atoms,an aryl group containing 6 to 12 carbon atoms, or hydrogen; or anorganic group containing from 1 to 50 carbon atoms; a is an integer from0 to 11; B is a substituted or unsubstituted benzophenone group; and bis an integer from 2 to 12.

The bridging group A can be a divalent group, or a polyvalent group with3 or more benzophenone moieties. The organic group, when present, can belinear, branched, cyclic (including fused or separate cyclic groups), oran arylene group (which can be a fused or non-fused polyaryl group). Theorganic group can contain one or more heteroatoms, such as oxygen,nitrogen, phosphorous, silicon, or sulfur, or combinations thereof.Oxygen can be present as, for example, an ether, ketone, aldehyde,ester, or alcohol.

The substituents of B, herein R″, when present, are individuallyselected from alkyl, aryl, alkoxy, phenoxy, or alicylic groupscontaining from 1 to 24 carbon atoms, or halides. Each benzophenonemoiety can have from 0 to 9 substituents.

Preferably, the combined molecular weight of the A and R″ groups is atleast about 30 g/mole. Substituents can be selected to render thephotoinitiator more compatible with the oxygen scavenging composition.

Examples of such benzophenone derivatives comprising two or morebenzophenone moieties include dibenzoyl biphenyl, substituted dibenzoylbiphenyl, benzoylated terphenyl, substituted benzoylated terphenyl,tribenzoyl triphenylbenzene, substituted tribenzoyl triphenylbenzene,benzoylated styrene oligomer (a mixture of compounds containing from 2to 12 repeating styrenic groups, comprising dibenzoylated 1,1-diphenylethane, dibenzoylated 1,3-diphenyl propane, dibenzoylated 1-phenylnaphthalene, dibenzoylated styrene dimer, dibenzoylated styrene trimer,and tribenzoylated styrene trimer), and substituted benzoylated styreneoligomer. Tribenzoyl triphenylbenzene and substituted tribenzoyltriphenylbenzene are especially preferred.

As stated above, the amount of photoinitiator can vary. In manyinstances, the amount will depend on the blend ratio or the particularoxygen scavenging polymer present in the oxygen scavenging composition,the wavelength and intensity of UV radiation used, the nature and amountof any antioxidants present in the oxygen scavenging composition, aswell as the type of photoinitiator. The amount of photoinitiator alsodepends on the intended use of the composition. For instance, if thephotoinitiator-containing composition is intended for use in a packagingarticle as a layer placed underneath a second layer which is somewhatopaque to the radiation used, more initiator may be needed. For mostpurposes, however, the amount of photoinitiator is in the range of 0.01to 10% by weight of the oxygen barrier layer.

Alternatively, or in addition, the energy-absorbing compound is amicrowave reactive material. Though not to be bound by theory, it isbelieved that microwave reactive materials absorb electromagneticradiation in the microwave range, and at least some of the energy of themicrowaves activates a chemical process or processes that result in theappearance of free radical electrons in the photoinitiator or fragmentsof the microwave reactive material produced by the chemical process orprocesses. Microwaves are readily produced by apparatus that can beconveniently included into package-formation or -filling procedures.Microwaves may also provide other useful activities, such as sterilizinga package prior to filling or activating other chemical reactions in thepackage which may be desired by the user.

In certain preferred embodiments of the invention, the microwavereactive material is selected from the group consisting of metalmaterials and materials comprising polar compounds. Preferred polarcompounds include water, peroxides, and peroxide solutions. Preferredperoxides include inorganic peroxides selected from the group consistingof sodium percarbonate, potassium percarbonate, calcium percarbonate,and sodium percarbonate, and organic peroxides selected from the groupconsisting of 2,5-dimethyl-2,5-di(benzoylperoxy) hexane; t-amylperoxyacetate; t-amyl peroxybenzoate; t-butyl peroxyacetate; t-butylperoxybenzoate; di-t-butyl diperoxyphthalate; 2,2-di-(t-butylperoxy)butane; 2,2-di(t-amylperoxy) propane; n-butyl 4,4-di(t-butylperoxy)valerate; ethyl 3,3-di-(t-amylperoxy) butyrate; ethyl3,3-(t-butylperoxy) butyrate; di-α-cumyl peroxide;α-α′-di-(t-butylperoxy) diisopropylbenzene;2,5-dimethyl-2,5-di-(t-butylperoxy) hexane; di-t-amyl peroxide; t-butylα-cumyl peroxide; di-t-butyl peroxide;2,5-dimethyl-2,5-di-(t-butylperoxy)-3-hexyne; di-t-butyl peroxide;di-t-amyl peroxide; and t-butyl hydroperoxide.

Where the microwave reactive material is a metal material, it cansuitably be in a form selected from the group consisting of foils,powders, meshes, staples, buttons, and fibers. In some particularlypreferred embodiments, the metal material comprises a powder selectedfrom the group consisting of aluminum, copper, iron, and oxides thereof.

The composition may further comprise other compounds, as will bedescribed in more detail below.

In another embodiment, the present invention relates to an oxygenbarrier layer of a packaging article, comprising:

an oxygen scavenging polymer comprising structure I:

X—R—X—O—CH₂—Ar—CH₂—O

,  (I)

wherein —R— is selected from the group consisting of C₁–C₂₄ alkyl,C₁–C₂₄ substituted alkyl, C₆–C₂₄ aryl, and C₆–C₂₄ substituted aryl; —Ar—is selected from the group consisting of C₆–C₂₄ aryl and C₆–C₂₄substituted aryl; and —X— is selected from the group consisting of nulland —C(═O)—;

a transition metal oxidation catalyst; and

an energy-absorbing compound selected from the group consisting ofmicrowave reactive materials and photoinitiators having a wavelength ofmaximum absorption of electromagnetic radiation from about 200 nm toabout 750 nm.

Packaging articles typically come in several forms including a singlelayer film, a multilayer film, a single layer rigid article, or amultilayer rigid article. Typical rigid or semirigid articles includeplastic, paper or cardboard cartons or bottles such as juice containers,soft drink containers, thermoformed trays, or cups, which have wallthicknesses in the range of 100 to 1000 micrometers. Typical flexiblebags include those used to package many food items, and will likely havethicknesses of 5 to 250 micrometers. The walls of such articles eithercomprise single or multiple layers of material.

The packaging article comprising the oxygen barrier layer can be used topackage any product for which it is desirable to inhibit oxygen damageduring storage, e.g. food, beverage, pharmaceuticals, medical products,corrodible metals, or electronic devices.

The packaging article comprising the oxygen barrier layer can comprise asingle oxygen barrier layer, or an oxygen barrier layer and additionallayers, such as an oxygen barrier layer not comprising a polymercomprising structure I, a food-contact layer, a structural layer, or anadhesive layer, alone or in any combination. Single layered packagingarticles can be prepared by solvent casting, injection molding, blowmolding, or by extrusion, among other techniques. Packaging articleswith multiple layers are typically prepared using coextrusion, injectionmolding, blow molding, coating, or lamination, among other techniques.

As stated above, the packaging article comprises an oxygen barrierlayer. In the oxygen barrier layer of the oxygen barrier packagingarticle, the polymer, the transition metal oxidation catalyst, and theenergy-absorbing compound are as described above. The polymer mayfurther comprise other units, as described above.

The polymer may comprise from about 5 wt % to 100 wt % of the oxygenbarrier layer. Preferably, the polymer comprises from about 20 wt % toabout 80 wt % of the oxygen barrier layer.

Other compounds are commonly used with oxygen scavenging polymers, inorder to enhance the functionality of the oxygen scavenging polymers instorage, processing into a layer of a packaging article, or use of thepackaging article. Such enhancements include, but are not limited to,limiting the rate of oxygen scavenging by the oxygen scavenging polymerprior to filling of the packaging article with a product, initiatingoxygen scavenging by the oxygen scavenging polymer at a desired time,limiting the induction period (the period between initiating oxygenscavenging and scavenging of oxygen at a desired rate), or rendering thelayer comprising the oxygen scavenging polymer stronger or moretransparent, among others. These compounds can be added to the oxygenbarrier layer or another layer of the packaging article, as appropriatefor the intended function of the compound.

Additives can be added to further facilitate or control the initiationof oxygen scavenging or oxygen barrier properties. Also, additionalcomponents such as a structural polymer or polymers can be added torender the layer more adaptable for use in a packaging article.Particular additives and components to be included in the oxygen barrierlayer can be readily chosen by the skilled artisan, depending on theintended use of the oxygen barrier layer and other parameters.

Antioxidants may be used to control scavenging initiation of oxygenscavenging in the oxygen barrier layer. An antioxidant as defined hereinis a material which inhibits oxidative degradation or cross-linking ofpolymers. Typically, antioxidants are added to facilitate the processingof polymeric materials or prolong their useful lifetime. In relation tothis invention, such additives prolong the induction period for oxygenscavenging in the absence of irradiation. When it is desired to commenceoxygen scavenging by the oxygen barrier layer, the packaging article(and incorporated photoinitiator or microwave reactive material) can beexposed to radiation.

Antioxidants such as 2,6-di(t-butyl)-4-methylphenol(BHT),2,2′-methylene-bis(6-t-butyl-p-cresol), triphenylphosphite,tris-(nonylphenyl)phosphite, vitamin E, tetrabismethylene3-(3,5-ditertbutyl-4-hydroxyphenyl)-propionate methane, anddilaurylthiodipropionate are suitable for use with this invention.

The amount of an antioxidant which may be present may also have aneffect on oxygen scavenging. As mentioned earlier, such materials areusually present in oxidizable organic compounds or structural polymersto prevent oxidation or gelation of the polymers. Typically, they arepresent in about 0.01 to 1% by weight of the composition. However,additional amounts of antioxidant may also be added if it is desired totailor the induction period as described above.

Other additives which can be included in the oxygen barrier layerinclude, but are not necessarily limited to, fillers, pigments,dyestuffs, stabilizers, processing aids, plasticizers, fire retardants,and anti-fog agents, among others.

Any other additives employed normally will not comprise more than 10% ofthe oxygen barrier layer by weight, with preferable amounts being lessthan 5% by weight of the oxygen barrier layer.

The oxygen barrier layer can also comprise film- orrigid-article-forming structural polymers. Such polymers arethermoplastic and render the oxygen barrier layer more adaptable for usein a packaging article. They also may, to some extent, have oxygenscavenging or oxygen barrier properties. Suitable structural polymersinclude, but are not limited to, polyethylene, low density polyethylene,very low density polyethylene, ultra-low density polyethylene, highdensity polyethylene, polyethylene terephthalate (PET), polyvinylchloride, ethylene-vinyl acetate, ethylene-alkyl (meth)acrylates,ethylene-(meth)acrylic acid, or ethylene-(meth)acrylic acid ionomers. Inrigid articles, such as beverage containers, PET is often used. Blendsof different structural polymers may also be used. However, theselection of the structural polymer largely depends on the article to bemanufactured and the end use thereof. Such selection factors are wellknown in the art. For instance, the clarity, cleanliness, effectivenessas an oxygen scavenger, oxygen barrier properties, mechanicalproperties, or texture of the article can be adversely affected by astructural polymer which is incompatible with the polymer comprisingstructure I.

Preferably, the structural polymer is PET. PET also exhibits oxygenbarrier properties.

In one particular preferred embodiment, the oxygen barrier layercomprises PET and benzenedimethanol PET. The weight ratio between PETand benzenedimethanol PET is preferably from 50:50 to 90:10. Such anoxygen barrier layer allows the incorporation of oxygen scavengingpolymers into a predominantly PET composition with high compatibilityand with the retention of the structural properties of PET. Further,polymers comprising structure I and ethylene terephthalate units alsohave oxygen barrier properties. A packaging article comprising such anoxygen barrier layer may be very effective in packaging beer, wine, orother oxygen-sensitive products with the potential for long shelf-lives.

Also, other oxygen barrier polymers can be included in the oxygenbarrier layer. Oxygen barrier polymers include poly(ethylene vinylalcohol) (EVOH), polyacrylonitrile, polyvinyl chloride (PVC),poly(vinylidene dichloride), and polyamides. PET is also an oxygenbarrier polymer, as described above.

The oxygen barrier layer may be in the form of a layer, film, liner,coating, sealant, gasket, adhesive insert, non-adhesive insert, orfibrous mat insert in the packaging article.

The packaging article comprising the oxygen barrier layer can comprise asingle oxygen barrier layer or an oxygen barrier layer and additionallayers. The additional layers of a multilayer material may comprise atleast one second oxygen barrier layer, i.e. a layer having an oxygentransmission rate equal to or less than 500 cubic centimeters per squaremeter (cc/m²) per day per atmosphere at room temperature (about 25° C.),wherein the second oxygen barrier layer does not comprise a polymercomprising structure I. Typical oxygen barrier layers comprisepoly(ethylene vinyl alcohol) (EVOH), polyacrylonitrile, polyvinylchloride (PVC), poly(vinylidene dichloride), polyethylene terephthalate(PET), polyamides, silica, or mixtures thereof. If the oxygen barrierlayer comprises EVOH, the packaging article preferably further comprisesa moisture barrier layer. Any polymers capable of providing a moisturebarrier and being formed into a layer of the packaging article may beused. The moisture barrier layer preferably comprises polyethylene,polyethylene terephthalate (PET), or a mixture thereof. However, becausethe oxygen barrier layer comprising a polymer comprising structure I maypossess adequate oxygen barrier properties, depending on the nature of—R— in structure I, polymers blended with the polymer comprisingstructure I, and the relative proportion of units having structure I toother units in either a copolymer or a blend, among others, a secondoxygen barrier layer may not be necessary.

The additional layers of a multilayer material may comprise at least onestructural layer, i.e. a layer imparting strength, rigidity, or otherstructural properties to the material. The structural layer can comprisepolyethylene, low density polyethylene, very low density polyethylene,ultra-low density polyethylene, high density polyethylene,polypropylene, polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), nylon, polyvinyl chloride, ethylene-vinyl acetate,ethylene-alkyl (meth)acrylates, ethylene(meth)acrylic acid,ethylene-(meth)acrylic acid ionomer, aluminum foil, or paperboard. PET,aluminum foil, or paperboard are preferred.

The additional layers of a multilayer material may comprise at least oneoxygen scavenging layer, i.e. a layer comprising a component thatconsumes oxygen. The oxygen scavenging layer can comprise squalene,polybutadiene, or ethylenic polymers comprising benzylic, allylic, orether-containing pendant groups, among other oxygen scavenging materialsknown to one of ordinary skill in the art. Ethylenic polymers comprisingcycloalkenyl pendant groups are preferred.

Other additional layers of the packaging article may include one or morelayers which are permeable to oxygen.

Further additional layers, such as adhesive layers, may also be used.Compositions typically used for adhesive layers include anhydridefunctional polyolefins and other well-known adhesive layers.

The oxygen barrier packaging article can be formed by any appropriatetechnique. By way of example, and not to be construed as limiting,forming the oxygen barrier packaging article will involve preparing theoxygen scavenging composition and other compounds to be includedtherein, heating the composition to a temperature above the meltingpoint of the polymer with stirring to produce a homogeneous melt, andsubsequent formation of the packaging article or oxygen barrier layerthereof from the melt. Single layered packaging articles can be preparedby solvent casting, injection molding, blow molding, or by extrusion,among other techniques. Packaging articles with multiple layers aretypically prepared using coextrusion, injection molding, blow molding,coating, or lamination, among other techniques. Not all of thesetechniques requiring formation of a melt comprising the polymer. Othertechniques for forming an oxygen barrier packaging article of thepresent invention may be apparent to one of ordinary skill in the art.

In yet another embodiment, the present invention relates to a method ofinitiating oxygen scavenging by an oxygen scavenging composition,comprising:

-   -   (a) providing an oxygen scavenging composition, comprising:        -   (i) an oxygen scavenging polymer comprising structure I:            X—R—X—O—CH₂—Ar—CH₂—O            ,  (I)        -    wherein —R— is selected from the group consisting of C₁–C₂₄            alkyl, C₁–C₂₄ substituted alkyl, C₆–C₂₄ aryl, and C₆–C₂₄            substituted aryl; —Ar— is selected from the group consisting            of C₆–C₂₄ aryl and C₆–C₂₄ substituted aryl; and —X— is            selected from the group consisting of null and —C(═O)—;        -   (ii) a transition metal oxidation catalyst; and        -   (iii) an energy-absorbing compound selected from the group            consisting of microwave reactive materials and            photoinitiators having a wavelength of maximum absorption of            electromagnetic radiation from about 200 nm to about 750 nm;            and

(b) exposing the oxygen scavenging composition to electromagneticradiation for a duration sufficient to initiate oxygen scavenging by theoxygen scavenging composition.

The oxygen scavenging composition is as described above. The oxygenscavenging composition can be a solid or a melt, and as a solid it canbe in the form of a packaging article or an oxygen barrier layerthereof. Preferably, the exposure is performed when the oxygenscavenging composition has been formed into a packaging article or anoxygen barrier layer thereof. More preferably, the exposure is performedno more than 1 hr prior to filling of the packaging article with aproduct.

In the performance of the method, the oxygen scavenging composition, inwhatever form it is provided, is exposed to electromagnetic radiation.Though not to be bound by theory, it is believed that electromagneticradiation is absorbed by the energy-absorbing component of the oxygenscavenging composition, and at least some of the energy of theelectromagnetic radiation drives chemical reactions that activate oxygenscavenging. Electromagnetic radiation of essentially any peak wavelength(i.e., the wavelength of maximum intensity) can be used.

The optimal duration of the exposure will depend on the peak wavelengthof the electromagnetic radiation, the wavelength of maximum absorptionof the energy-absorbing compound, the intensity of the electromagneticradiation, and the geometry of the radiation source and the composition,among other parameters apparent to one of ordinary skill in the art. Theduration can be readily adjusted by adjusting one or more of theparameters as the user may desire.

The closer the peak wavelength of the electromagnetic radiation is tothe wavelength of maximum absorption of the energy-absorbing compound,the greater the fraction of the electromagnetic radiation's energy thatwill be absorbed. Thus, either less intense electromagnetic radiation, ashorter duration of exposure, or both are possible, relative to thesituation where the peak wavelength of the electromagnetic radiation isfurther from the wavelength of maximum absorption of theenergy-absorbing compound. Preferably, the electromagnetic radiation hasa peak wavelength from about 50 nm shorter than the wavelength ofmaximum absorption of the energy-absorbing compound to about 50 nmlonger than the wavelength of maximum absorption of the energy-absorbingcompound. More preferably, the electromagnetic radiation has a peakwavelength from about 10 μm shorter than the wavelength of maximumabsorption of the energy-absorbing compound to about 10 nm longer thanthe wavelength of maximum absorption of the energy-absorbing compound.

The electromagnetic radiation can be provided by any appropriate source.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventor to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

EXAMPLES

Materials: Cobalt oleate and cobalt neodecanoate were obtained fromShepherd Chemical Co. Tribenzoyl triphenylbenzene (BBP³) photoinitiatorwas obtained from Chevron Phillips Chemical Co. Poly(ethyleneterephthalate) (PET) was obtained from PLM Lidkoping AB.1,4-Benzenedimethanol was provided by Century Multech Inc. Dimethyladipate and dimethyl terephthalate were purchased from Aldrich. Titaniumisopropoxide was obtained from Elf Atochem Co.

Example 1 Preparation of Oxygen Scavenging Compositions ComprisingBenzenedimethanol Containing Polyesters

Synthesis of Poly(1,4-benzenedimethylene adipate) (Composition 1): To apressure-resistant reactor were added 1000 parts of dimethyl adipate,793 parts of 1,4-benzenedimethanol and 1 part of titanium isopropoxide.The reactor was flushed with nitrogen and heated to 190° C. After 1 hourthe temperature was raised to 275° C., the nitrogen flush was stoppedand a vacuum line attached. A vacuum pump was activated and the reactioncontinued for 1 hour at high vacuum. The reaction was then allowed tocool to room temperature under vacuum. The product was dissolved inchloroform and precipitated in an excess of methanol. The polymer wascollected by filtration and dried in a vacuum oven overnight. Thepolyester obtained had a peak melting point of 74° C. as measured by DSC(10° C./min.).

Synthesis of Poly(1,4-benzenedimethylene terephthalate-co-adipate)(Composition 2): To a pressure resistant reactor were added 1000 partsof dimethyl terephthalate, 298.8 parts of dimethyl adipate, 949.2 partsof 1,4-benzenedimethanol, and 3 parts of titanium isopropoxide. Theflask was sealed and flushed under nitrogen, then warmed toapproximately 150° C. After 1 hour the reaction temperature wasincreased to 220° C., and held at that temperature for 1 hour. Thereaction temperature was then increased to 250° C. Then, 3 parts oftriphenyl phosphite were added. After 1–2 hours, the nitrogen flow wasstopped, and the flask was connected to a high-vacuum pump. The pressurewas lowered to 1 torr, and the reaction was continued for 1–2 hour. Thetemperature was finally raised to 270–280° C. Afterwards the vacuum linewas disconnected and the polymer was poured onto an aluminum pan tocool, under nitrogen blanket. The product was a low molecular weightpolymer with an inherent viscosity of 0.2. The polymer was then groundinto smaller particle sizes and heated at 240° C. under high vacuum for2 hours. This resulted in a high molecular weight polymer with aninherent viscosity of 0.6. The polymer had a melting range of 208–230°C. as measured by DSC (10° C./min.).

Formulation of Oxygen Scavenging Composition by Solution Method(Composition 1): 100 Parts of poly(1,4-benzenedimethylene adipate)prepared by the above procedure was dissolved in chloroform to make up a20% solution. To the solution was added 0.1 part of cobalt II catalyst(as oleate salt) and 0.1 part of photoinitiator (BBP³). After a clearblue-colored solution was obtained, the solution was poured onto a flatsurface and the solvent was allowed to evaporate at room temperature.The obtained polymer film was further dried in a vacuum over night,which gave an optically clear film and was used for the subsequentdemonstration for oxygen scavenging activity.

Formulation of Oxygen Scavenging Composition by Melt Process(Composition 2): Poly(1,4-benzenedimethylene terephthalate-co-adipate)prepared by the above procedure was processed on a Haaka twin screwextruder at 260° C. and the polymer strand was then pelletized. Toevaluate the compatibility of the prepared polyester with commercialPET, 30 parts of poly(1,4-benzenedimethylene terephthalate-co-adipate)pellets and 70 parts of commercial PET pellets were mixed in acontainer. To the mixture, 0.01 part of cobalt II catalyst (asnoedecanoate slat) and 0.01 part of photo initiator (BBP3) were addedand thoroughly mixed. It was found to be usually more efficient to addthe catalyst and photo initiator as a solution with minimal amount ofmethylene chloride. The mixture was compounded on a Haaka twin screwextruder at 260° C. and a screw speed of 40 rpm. This gave an opticallyclear strand, an indication of desired compatibility between theprepared polyester and the commercial PET.

Example 2 Oxygen Scavenging Activity of Benzenedimethanol-ContainingPolyester

The oxygen scavenging activity was demonstrated by monitoring thereduction in oxygen concentration as a result of consumption of oxygenby the prepared film sample. Thus, 0.5 gram of film sample made frompoly(benzenedimethanol adipate) was first activated by exposure to a UVlight at 254 nm for 85 sec, which resulted in a dosage of 100 mJ/cm².The irradiated film sample was then sealed in an aluminum bag and filledwith 300 cc of air and kept at room temperature over time. The reductionin oxygen concentration over time was analyzed on a Mocon 450 HeadspaceAnalyzer by taking 5 cc of gas from the bag at different time intervals.Results of a duplicated test are shown in FIG. 1. The figure indicatesthat the oxygen was consumed rapidly, and more than 50 cc oxygen wasscavenged for each gram film sample.

Not to be bound by the theory, it is believed that the methyleneadjacent to the benzene ring on the benzenedimethylene unit wasresponsible for reacting and consuming oxygen, catalyzed by the cobaltsalt. It is believed that the stabilization effect of the benzene ringmade proton abstraction at the methylene adjacent to the benzene ringmore feasible, which is the rate-limiting step in the oxidationreaction. The active scavenging capability of the invented compositionswill make it feasible to enhance the oxygen barrier performance byincorporating such compositions into the packaging structure since theyare capable of scavenging and intercepting the oxygen transmission fromthe environment into the packaging structure. Additional benefit can beachieved from the invented compositions because they are compatible withcommercial PET, a dominant packaging material for the rigid packagingapplication where the clarity is an important property to be maintained.Furthermore, the functional monomer, benzenedimethanol, can be used asfeed stock in the current PET manufacturing process with minimum impacton the process, it will be highly economical to produce the functionalPET product, and turn it into active oxygen barrier material byincorporating the appropriate amount of cobalt catalyst and photoinitiator during the down stream processing.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe method described herein without departing from the concept, spiritand scope of the invention. More specifically, it will be apparent thatcertain agents which are both chemically and physiologically related maybe substituted for the agents described herein while the same or similarresults would be achieved. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by theappended claims.

1. An oxygen barrier packaging article, comprising: an oxygen scavengingpolymer comprising structure I:

X—R—X—O—CH₂—Ar—CH_(2—)O

,  (I)  wherein —R— is selected from the group consisting of C₁–C₂₄alkyl, C₁–C₂₄ substituted alkyl, C₆–C₂₄ aryl, and C₆–C₂₄ substitutedaryl; —Ar— is selected from the group consisting of C₆–C₂₄ aryl andC₆–C₂₄ substituted aryl; and —X— is selected from the group consistingof null and —C(═O)—; a transition metal oxidation catalyst; and anenergy-absorbing compound selected from the group consisting ofmicrowave reactive materials and photoinitiators having a wavelength ofmaximum absorption of electromagnetic radiation from about 200 nm toabout 750 nm.
 2. The packaging article of claim 1, wherein the oxygenscavenging polymer consists essentially of units having structure I. 3.The packaging article of claim 1, wherein the transition metal catalystis a cobalt salt.
 4. The packaging article of claim 3, wherein thecobalt salt is selected from the group consisting of cobalt oleate,cobalt stearate, and cobalt neodecanoate.
 5. The packaging article ofclaim 1, wherein the energy-absorbing compound is a photoinitiatorselected from the group consisting of benzophenone derivativescontaining at least two benzophenone moieties and having the formula:A_(a)(B)_(b) wherein A is a bridging group selected from the groupconsisting of sulfur, oxygen, carbonyl, —SiR″₁—, wherein each R″ isindividually selected from alkyl groups containing from 1 to 12 carbonatoms, aryl groups containing 6 to 12 carbon atoms, or alkoxy groupscontaining from 1 to 12 carbon atoms, —NR′″—, wherein R′″ is an alkylgroup containing 1 to 12 carbon atoms, an aryl group containing 6 to 12carbon atoms, or hydrogen, and an organic group containing from 1 to 50carbon atoms; a is an integer from 0 to 11; B is a substituted orunsubstituted benzophenone group; and b is an integer from 2 to
 12. 6.The packaging article of claim 5, wherein the photoinitiator is selectedfrom the group consisting of dibenzoyl biphenyl, substituted dibenzoylbiphenyl, benzoylated terphenyl, substituted benzoylated terphenyl,tribenzoyl triphenylbenzene, substituted tribenzoyl triphenylbenzene,benzoylated styrene oligomer, and substituted benzoylated styreneoligomer.
 7. The packaging article of claim 1, further comprising anantioxidant.
 8. The packaging article of claim 7, wherein theantioxidant is selected from the group consisting of2,6-di(t-butyl)-4-methylphenol (BHT),2,2′-methylene-bis(6-t-butyl-p-cresol), triphenylphosphite,tris-(nonylphenyl)phosphite, vitamin E, tetra-bismethylene3-(3,5-ditertbutyl-4-hydroxyphenyl)-propionate methane, anddilaurylthiodipropionate.
 9. The packaging article of claim 1, furthercomprising an oxygen barrier polymer selected from the group consistingof poly(ethylene vinyl alcohol) (EVOH, polyacrylonitrile, polyvinylchloride (PVC), poly(vinylidene dichloride), polyethylene terephthalate(PET), and polyamide.
 10. The packaging article of claim 1, furthercomprising an oxygen barrier layer.
 11. The packaging article of claim10, wherein the oxygen barrier layer comprises poly(ethylene vinylalcohol) (EVOH), polyacrylonitrile, polyvinyl chloride (PVC),poly(vinylidene dichloride), polyethylene terephthalate (PET), orpolyamide.
 12. The packaging article of claim 11, wherein the oxygenbarrier layer comprises EVOH, and the packaging article furthercomprises a moisture barrier layer.
 13. The packaging article of claim12, wherein the moisture barrier layer comprises polyethylene,polyethylene terephthalate (PET), or a mixture thereof.
 14. Thepackaging article of claim 1, further comprising a structural layer. 15.The packaging article of claim 14, wherein the structural layercomprises polyethylene, low density polyethylene, very low densitypolyethylene, ultra-low density polyethylene, high density polyethylene,polypropylene, polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), nylon, polyvinyl chloride, ethylene-vinyl acetate,ethylene-alkyl (meth)acrylates, ethylene-(meth)acrylic acid,ethylene-(meth)acrylic acid ionomers, aluminum foil, or paperboard. 16.The packaging article of claim 15, wherein the structural layercomprises PET, aluminum foil, or paperboard.
 17. The packaging articleof claim 1, wherein the oxygen scavenging polymer, the transition metaloxidation catalyst and energy-absorbing compound comprise a liner,coating, sealant, gasket, adhesive insert, non-adhesive insert, orfibrous mat insert in the packaging article.
 18. The packaging articleof claim 1, wherein the packaging article is in the form of a singlelayer film, a multilayer film, a single layer rigid article, or amultilayer rigid article.